1. Analysis of Reheat Rankine Cycle
P M V Subbarao
Professor
Mechanical Engineering Department
Means to Eliminate Hurdles while Adopting high Live Steam Pressures ……

2. Hurdles in Implementation of High Pressure Cycles
Tmax = 546C &Tmin=40 C
xturbine-exit
Main SteamPressure, MPa

3. Reheating of Steam to Enhance Quality at the Turbine Exit
Single Turbine drum

4. Reheaters
The pressure drop inside reheater tubes has an adverse effect on the efficiency of turbine.
Pressure drop through the reheater should be kept as low as possible.
Higher pipe diameter and low steam will velocities can lower the pressure drop, but leads to higher capital cost.
Techno-economically viable Range: Tube diameter : 42 – 60mm.

5. Cost to Benefit Ratio of Reheat Cycle

6. Analysis of Reheat Cycle
Consider reheat cycle as a combination of Rankine cycle and horn cycle.
Cycle = Cycle ’-1 + Cycle 4’ ’.
Therefore, 4’ 6

7. Analysis of Horn Cycle Horn Cycle: 4’ – 4 Isentropic Compression.
4 – 5 Isobaric Heat Addition.
5 – 6 Isentropic Expansion
6 – 4’ Isobaric(thermal) cooling.
4’ 6

8. Condition for Development of Efficient Reheat Cycle

9. Change in Efficiency due to Reheating
Condition for increased efficiency:
Select appropriate reheat pressure, pRH, such that left hand side is maximum.

10. Selection of Reheat Pressure
pmax= 15 MPa
Tmax= 550 0C
Tsat= C

11. Effect of Reheat Pressure
Dh,%
1.0
0.2
0.4
0.6
0.8
~0.3
prh/pmax

12. Optimal Selection of Reheat Point

13. Reheating : A Means to implement High Live Steam Pressure
Supercritical
593/6210C
593/5930C
565/5930C
565/5650C
538/5650C
Improvement in Efficiency, %
538/5380C

14. Effect of Reheating on Overall Tm,in

15. Procedure to Determine Optimum Reheat Pressure
Calculate the efficiency of Rankine cycle, hRankine.
Calculate mean effective temperature of heat addition, Tm,in using
Find out pressure corresponding to Tm,in and entropy at HP turbine exit.
Add reheating at this pressure and calculate efficiency of the Reheat Cycle.
Repeat above steps for few iterations.

16. pmax= 15 MPa
Tmax= 550 0C
Tsat= C

17. Super Critical Cycle ~ 1990

18. Effect of Various Steam Parameters on Reheat Cycle

19. Ultra Supercritical Installations of The World